Academic journal article Attention, Perception and Psychophysics

Somatosensory Prior Entry

Academic journal article Attention, Perception and Psychophysics

Somatosensory Prior Entry

Article excerpt

The perceived timing of sensory events does not necessarily match the actual timing. In the present study, we investigated the effect of location of attention on the perceived timing of somatosensory stimuli. Participants judged the temporal order of two taps, delivered one to each hand, with taps presented at different elevations (upper and lower) on the opposing hands. The task was to discriminate the elevation of the tap presented first (or second). This vertical discrimination task was orthogonal to the horizontal attentional cuing manipulation, removing the response bias confound that has undermined earlier studies investigating the impact of attention on the perceived timing of sensory stimuli. We manipulated spatial attention either (1) exogenously (Experiment 1) in 13 participants, using brief taps to either the left or right hand, or (2) endogenously (Experiment 2) in 22 participants, using centrally presented symbolic cues. The results supported the hypothesis that attended stimuli are perceived more rapidly than unattended stimuli. This effect was larger when attention was exogenously manipulated. Previous research has demonstrated a similar effect for visual stimuli. The present study, which extends this result to somatosensory perception, indicates that the phenomenon may represent a more global feature of the perceptual system, which is possibly mediated by a common modality-independent mechanism.

Our senses provide many forms of information to the brain. One of the most fundamental categories of sensory data is the timing (e.g., onset, duration, order, rate) of stimuli in the environment. Our brains use this timing information to perceive the environment around us. An illustrative example is the small time difference in the arrival of soundwaves from a singular sound source to the left and right ears, which is used by the brain to locate the source of the sound (Yamada, Kaga, Uno, & Shindo, 1996). The brain's use of temporal information extends into many other aspects of perception, from the comprehension of speech to the determination of the direction and velocity of objects in the environment, the integration of sensory information from different modalities, the location of the body in space (Ehrsson, Spence, & Passingham, 2004), and the ability to distinguish between self-caused versus externally caused events in the environment (Cunningham, Billock, & Tsou, 2001; Wegner & Wheatley, 1999). Despite the ubiquity and usefulness of sensory temporal information, the way in which the brain codes this information is largely unknown.

A significant gap in our knowledge in this area is a basic account of the relationship between the actual timing of stimulus events and the perceived timing of those events, the factors that influence this relationship, and the manner (i.e., where, when, and how) in which this influence occurs. Central to such an account is the role of attention, particularly in light of the opportunity that attention presents in "connecting the mental level of description of processes used in cognitive science with the anatomical level common in neuroscience" (Posner & Petersen, 1990, p. 25). Can paying attention to a stimulus affect the time at which that stimulus is perceived, and if so, how? One influential claim concerning the nexus between attention and perceptual latency has been that attending to a stimulus accelerates its perception: "The object of attention comes to consciousness more quickly than the objects which we are not attending to" (Titchener, 1908, p. 251). This claim is known as the doctrine of prior entry.

The question of how attention can affect the perceived timing of events is of interest both clinically and experimentally. Clinically, Rorden, Mattingley, Karnath, and Driver (1997) showed that patients with left-sided neglect-a failure to attend and orient to the left side of space-had dramatic abnormalities in the time that they perceived stimuli in the neglected hemifield, with significantly delayed perception of such stimuli as compared with the perception of stimuli presented in the normal hemifield. …

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